The invention relates to groove rolling of piping, tubing, and fitting elements.
A grooved end pipe coupling, e.g. of the type illustrated in FIGS. 1 and 1A, is used for joining together ends of pipe elements in a leak tight assembly by use of grooves that are cut, cast or formed in the ends of the pipe elements. The terms "pipe elements", "pipes", and "piping", refer herein to sections of pipes, tubes, fittings, valves bodies, and the like, both in the plural and the singular. Referring to FIGS. 2 and 3, critical parameters of a grooved end connection include: the gasket seat diameter, D.sub.s, groove diameter, D.sub.g, gasket seat width, W.sub.s, and groove width, W.sub.g. In the case of wrought metal piping elements, e.g. tubing, fittings, or valve bodies, the grooved end of the piping element, P, is conventionally produced by either a cutting (machining) operation or a rolling (contour roll forming) operation as shown in piping element P.sub.CUT, of FIG. 2, and piping element P.sub.ROLL, of FIG. 3, respectively. In the case of a cast fitting or valve body, the grooved end connection is normally either cut in the configuration of a piping element, P.sub.CUT shown in FIG. 2, or cast in the dual outward step configuration of a piping element, P.sub.CAST, shown in FIG. 4. Each piping element includes a groove 30 a distance at least W.sub.s from an end. P.sub.ROLL includes an indented region 32 on its inner surface underneath groove 30.
Cut grooves for use with grooved end pipe couplings are typically prepared by the use of a turning process.
Roll grooves for use with grooved end pipe couplings have been prepared by an apparatus similar in function to that described in Kunsman U.S. Pat. No. 3,995,466 and Dole U.S. Pat. No. 5,279,143. Both of these patents describe a means for contour roll forming a groove in the end of the pipe element by which a segment of the pipe is press formed or stretched into the desired configuration by forcing a shaped die roller located outside of the pipe against a form roller located inside of the pipe.
Other examples of contour roll forming of pipes are presented in Constantine, Great Britain Patent 18201, Pritchett, et al. U.S. Pat. No. 3,191,416 and Vaill, et al. U.S. Pat No. 3,290,914. Although these latter three patents describe devices which force a die roller located inside the pipe against a form located outside of the pipe, the contour roll forming principle is the same as for the previous two patent references. That is, the pipe is locally shaped by radial press forming or stretching, into the desired contour.
Referring again to FIGS. 1, 1A, and 2-4, a typical grooved end pipe coupling assembly 10 consists of two or more housing segments 12, 14, a gasket 16, and fastening means, e.g. nuts 18 and bolts 20, for securing assembly 10 together with the end connections to be joined. Housing segments 12, 14 have keys 22 around the inner periphery at both ends, a shoulder 24 also around and just inside each key, and a gasket cavity 26. Keys 22 fit into grooves 30 formed in each pipe end to axially and transversely retain the end connections. Keys 22 and shoulders 24 are involved to varying degrees in maintaining coupling assembly 10 generally centered about the grooved end connection. Shoulder 24 fits closely around the gasket seat diameter to prevent gasket 16 from extruding outwardly under the internal pressure of the piping system, gasket 16 being retained in gasket cavity 26 and producing a seal on gasket seat surfaces 34 to form a leak tight assembly.